作业4，21

#include<iostream>#include<string>using namespace std;class student{private:int number;string name;float score;static int count;static float sum;static float ave;public:student(int num,string n,float sc);void show(){cout<<"学号："<<number<<endl;    cout<<"姓名："<<name<<endl;    cout<<"成绩："<<score<<endl;}void show_count_ave(){cout<<"学生人数："<<count<<endl;cout<<"平均成绩："<<ave<<endl;}};student::student(int num,string n,float sc){number=num;name=n;score=sc;++count;sum=sum+score;ave=sum/count;}int student::count=0;float student::sum=0.0;float student::ave=0.0;int main(){student stu1(101,"liming",88);stu1.show();stu1.show_count_ave();student stu2(102,"chenhua",79);stu2.show();    stu2.show_count_ave();student stu3(101,"wuyan",95);stu3.show();stu3.show_count_ave();return 0;}